Television system



March 16; 1943. H R0: 2,313,971

TELEVISION SYSTEM Filed Aug. 3, 1940 Patented Mar. 16, 1943 UNITED STATES PATENT GFFEQE TELEVISION SYSTEM John H. :Roe, :Merchantville, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application August 3, 1940, Serial No. 350,186

1 Claim.

oscillator at the receiving station that generates I a voltage having a sawtooth wave and a frequency insynchronism with the-transmitted deflection nulsesignals. Heretofore it has been the general practice to amplify the saw-tooth wave generated by the oscillator and'apply this amplified signal to the defiectionpmeans of the picture tube with such ,a polarity that the signal current through the-deflection yoke ofthe picture tube increased slowly during a greater portion of a complete saw-tooth cycle and decreased to its minimum value almost instantaneously.

According to this invention, the amplified sawtooth wave deflection signal isgapplied tothe'defiecting means of the picture tubewith such a polarity that the signal current through the defiection yoke ofthepicture tube decreases slowly-durin'g a greater portion of a complete sawtooth cycleand increases to its maximum value almost instantaneously. This permits the additionof one stage of amplification which provides .anadditional coupling circuit to allowthe additionof wave shaping circuits. This makes'itpossible'toobtainpractically flawless linearity in the rateof scanning.

Apentode amplifier output tube is usedwithout danger of sparking over because the maximum peak voltage across thedefiection coil is limited to theplatesupply voltage; that is, the voltage .pulse caused by the discharge of the stored up energy in the deflection coil of the picture tube is in a. negative direction.

The principal obj ect of this invention is to provide adefiection' circuit for a picture tubewhich gives a .very nearly linear scanning rate.

Another object of this invention is :to provide an improved deflection circuit wherein wave shaping circuits may be employed.

Still another object of this invention is to provide an improved system wherein the electron beam deflection current flowing through the defiection coils of a picture tube decreases progressively over a greater portion of the saw-tooth wave cycle asthe picture is scanned fromthe top to the bottom.

Other and incidental objects of the invention will be apparent to those skilled in the art from consideration of the following specification in connection with the accompanying drawing in which Figure 1 is a circuit diagramshowing one form of this invention, and

Figure 2 contains a number of .graphicalrepresentations illustrating the operation ,of thisinvention.

Referring to Fig. .1, the vertical deflection pulses are received from the synchronizing pulse separator in a television receiver at terminal I.

The synchronizing pulsetseparator may be pfzthe type shown and described in Tolson Patent No. 2,207,839, granted July'16,.'194= 0. These pulsesare applied to the control electrode 3 of thesaw-tooth wave generator dischargedevice ,5 through coupling condenser 1 and transformer vwinding 9. The first anode I l of the blockingoscillator tube 5 is provided with a positive potential through resistor 13, and by-pass condenser l5 and-transformer winding l! which is'inductively coupled to the previously mentioned transformerwinding 9. The free vibration period or fundamental frequency of the saw-tooth wave generator is manually controlled by resistances l9 and A21. The control electrode disconnected to the sec- 0nd control electrode 23 which governs the current fiow1frcm thecathode 25 to the-anode 21 which receives its potential through resistance 29 and manually adjustable resistance 3| which is employed to control theamp'litude of the output of the sawtooth wave generator. A detailed description of the operation of thistype ofoscillator is given in the patent to Tolsonand Duncan No. 2,101,520, granted December -7, 1937.

The deflection signal isthen subjected to a first shaping circuit comprising a condenser 35 in series with the resistance ,37. This shaping circuit is followed-by a second shaping circuit of thesirnilar type having coridensrliil in series with-resistance 4|. Ithas-beenfound that it is not possible to combine thesetwdshaping circuits I because each circuit individually reacts upon the other sc -that the combined effect will provide the desired wave shape. This combined effect will be more readily understood when one considers that the anode resistors 20 and 3| are also included as part of the shaping circuit.

The signal is then applied to the control electrode 43 of the amplifier tube 45 through coupling condenser 41. A grid leak is provided for the amplifying tube 45 and the control electrode bias is supplied in the circuit of the cathode 5| through resistor 53 and by-pass condenser 55. The anode 51 of this amplifier tube 55 is supplied with its potential through resistances 59 and 60. Resistance 69 is of high value compared with resistance 59 and is shunted by condenser 62 which provides another shaping circuit increasing the flexibility of the amplifier. The signal is then fed to the control electrode 6| of the output tube 63 through coupling condenser 65. The control electrode bias for tube 63 is supplied from cathode 64 through resistances 66 and 68.

The signal from the anode 61 of the output tube 63 is fed to the vertical deflection coils 69 and H of the picture tube 13 which has the usual cathode heater 15, cathode Tl, control electrode 79, first anode 81, and second anode 83. Anode 5? is supplied with its potential through inductance 85 and resistance 31. The circuit through The invention thus involves a combination of wave shaping circuits comprising a series capacitor 35, resistor 31 and series capacitor 39, resistor 4| inserted in the output circuit of the blocking oscillator, and resistances 59, 69 and condenser 62 in the anode circuit of tube 45 for modifying the wave shapes as represented by the solid lines in each of curves, a, b, c, and d at the same points as given above for the voltage curves without the combination of wave shaping circuits. The combination of the two wave shaping circuits in the output circuit of the blocking oscillator tube curve the sloping portion of the saw-tooth voltage wave output of the blocking oscillator as represented by the solid line of curve a.

This formation of the sloping portion of the curve provides a corresponding change in the ing a relatively high L/R ratio is used, the peak voltage across the deflecting yoke coil 69 and H would exceed the plate supply voltage and the anode Bl of tube 63 would become negative with respect to cathode 64 of tube 63.

In Fig. 2, the brokenline in each of the curves shows the results obtained when only one shaping circuit of the type comprising condenser and resistance 3'! is used in the anode circuit of the blocking oscillator tube 5.

The broken line shown by curve a represents the voltage output wave of the blocking oscillator. It should be noticed here that the sloping portion of the curve is substantially a straight line. The application of this signal voltage .to the control electrode 43 of the. amplifying tube 45 results in an output voltage from the anode 51 having a shape as indicated by the solid line in curve 17, whose sloping portion takes on a decided curve because of non-linearity of coupling circuits and tube characteristics. This signal is the applied to the control electrode 6| of the output tube 63 which produces in its output circuit at anode 61 the voltage curve as indicated by the solid line of the curve 0, whose sloping portion is not a straight line, and consequently the resulting current through the vertical deflecting coils 69 and H, shown by the solid line of curve :1 also shows a curve in the sloping portion of the saw-tooth wave.

' It will be noticed, from a study of curve 11, that, without employing the second wave shaping circuit as taught by this invention, the current increases non-uniformly over the greater portion of the complete saw-tooth wave cycle, thus resulting in a non-uniform scanning or a bunching of scanning lines at one edge of the image.

curve of the voltage output from tube 45 when another shaping circuit comprising resistances 59, 60 and capacity 62 is included as represented by the'solid line in curve b. It will be noticed,

however, that in curve I) the application of the wave shaping circuits reduces the curve of the voltage so that the output of the tube 63 pro-- vides a voltage curve which is substantially straight over the sloping portion of the saw tooth wave cycle as shown by the solid line in curve 0.

It follows that the current through the deflection coil will decrease gradually at a uniform rate over the sloping portion of the saw-tooth cycle when the wave shaping circuits previously described are inserted in the circuit. This results in a uniform separation of scanning lines which, of course, ultimately results in an image of better detail.

While one system for carrying this invention into efiect has been indicated and described, it will be apparent to one skilled in the art that this invention is by no means limited to the particular organization shown and described, but that many modifications may be made without departing from the scope thereof as set forth in the appended claim.

I claim as my invention:

In a television system, an electric discharge device having an anode and a cathode, an output circuit including an anode resistor for said discharge device, a direct-current voltage source connected between said cathode and said anode resistor to apply a positive voltage to said anode, at least two wave shaping circuits connected in parallel with each other and each comprising a resistor and a condenser only, said condenser and said resistor of each of said wave shaping circuits being connected in series with each other, said parallel combination of wave shaping circuits being connected between said anode and said cathode whereby said condensers receive a charge through said anode resistor, means for holding said discharge tube normally non-conducting from anode to cathode, and means for producing and so applying recurring 'voltage pulses to said discharge tube that said condensers discharge through said tube during the occurrence of each voltage pulse.

JOHN H. ROE. 

